Introduction to Photoshop CS
Photoshop is a raster program, also known as a paint or image manipulation program. Adobe Photoshop is the industry standard software of raster programs. There are many other image manipulation programs include Macromedia's Xres, Paint Shop Pro and Corel's Photo Paint, all similar in content to Photoshop.
Paint and image-editing software, such as Adobe Photoshop, generate bitmap images, Also called raster or pixel based imagery. The images use a grid of small squares, known as pixels, to represent graphics. Each pixel in a bitmap image has a specific location and colour value assigned to it. For example, a bicycle tyre in a bitmap image is made up of a collection of pixels in that location, with each pixel part of a mosaic that gives the appearance of a tyre.
When working with bitmap images, you edit pixels rather than objects or shapes. Because they can represent subtle gradations of shades and colour, bitmap images are the most common electronic medium for continuous-tone images, such as photographs or images created in painting programs. Bitmap images are resolution dependent; they represent a fixed number of pixels. As a result, they can appear jagged and lose detail if they are scaled on-screen or if they are printed at a higher resolution than they were created for. Bitmap images are good at reproducing the subtle shading found in continuous-tone images, such as photographs. However, bitmap images do not enlarge well and can show jagged edges when magnified or output to higher-resolution devices.